Tcpdump

tcpdump is a data-network packet analyzer computer program that runs under a command line interface. It allows the user to display TCP/IP and other packets being transmitted or received over a network to which the computer is attached. Distributed under the BSD license, tcpdump is free software. Tcpdump works on most Unix-like operating systems: Linux (including Android and embedded distribution such as OpenWrt), Solaris, FreeBSD, DragonFly BSD, NetBSD, OpenBSD, macOS, HP-UX 11i, and AIX. In those systems, tcpdump uses the libpcap library to capture packets. The port of tcpdump for Windows is called WinDump; it uses WinPcap, the Windows version of libpcap. tcpdump was originally written in 1988 by Van Jacobson, Sally Floyd, Vern Paxson and Steven McCanne who were, at the time, working in the Lawrence Berkeley Laboratory Network Research Group. By the late 1990s there were numerous versions of tcpdump distributed as part of various operating systems, and numerous patches that were not well coordinated. Michael Richardson (mcr) and Bill Fenner created www.tcpdump.org in 1999. tcpdump prints the contents of network packets. It can read packets from a network interface card or from a previously created saved packet file. tcpdump can write packets to standard output or a file. It is also possible to use tcpdump for the specific purpose of intercepting and displaying the communications of another user or computer.